Emerson Rosemount CT5400, Installation, Operation And Maintenance Manual

Page: 167 / 176

Appendix A
Theory of Operation
A.1 Overview
The Rosemount
™
CT5400 is a gas sensor system that can be configured to measure the
concentrations of multiple small molecules carried in the gas sample. The types of
molecules that are measured depend on the system configuration.
The analyzer can be configured to detect and measure up to twelve gases, with ranges
varying from volume to percent (%) volume levels. A detailed description of the system is
given in Detailed System Specification of this manual.
A.2 Quantum Cascade Laser measurement
principle
The analyzer uses six Quantum Cascade Lasers to detect and measure the gases. Each
Quantum Cascade Laser (QCL) measures between one and three gases.
Inside the QCL, which is about the size of a pin head, electrons cascade down a series of
quantum wells, producing a photon at each step. This cascade of electrons can produce
between 20 and 100 photons per electron, giving QCLs higher output power than
traditional semi-conductor lasers.
The lasing wavelength of a QCL is determined by adjusting the physical thickness of the
semiconductor layers, giving access to high power lasers covering the mid-infrared
spectral region. A QCL has no need for cryogenic cooling, has excellent spectral quality in
chirped mode, and good tuneability.
Theory of Operation
Installation, Operations, and Maintenance Manual 147